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Fix React rendering errors to show 404 page instead of Hey Fernie page #4140

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Fix React rendering errors to show 404 page instead of Hey Fernie page #4140

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54b8392
Fix React rendering errors to show 404 page instead of Hey Fernie page
devin-ai-integration[bot] Oct 16, 2025
2eaa557
Fix import order for biome lint
devin-ai-integration[bot] Oct 16, 2025
570fa4d
Add missing features to error boundary: analytics tracker and return …
devin-ai-integration[bot] Oct 16, 2025
4e789aa
Address Vercel Agent feedback: improve error boundary UX
devin-ai-integration[bot] Oct 16, 2025
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35 changes: 35 additions & 0 deletions packages/fern-docs/bundle/src/app/[host]/[domain]/error.tsx
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Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
"use client";

import { FernButton } from "@fern-docs/components/FernButton";
import GradientExclamation from "@fern-docs/components/GradientExclamation";
import { HiddenSidebar } from "@fern-docs/components/theming/HiddenSidebar";
import { useEffect } from "react";

import { NotFound404Tracker } from "@/components/analytics/NotFound404Tracker";
import ReturnHomeButton from "@/components/ReturnHomeButton";

export default function ErrorBoundary({ error, reset }: { error: Error & { digest?: string }; reset: () => void }) {
useEffect(() => {
console.error(`[domain-error-boundary] ${JSON.stringify(error)}`);
}, [error]);

return (
<>
<NotFound404Tracker />
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The error boundary incorrectly uses NotFound404Tracker, which will track all rendering errors as "not_found" events in analytics instead of just actual 404 errors.

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📝 Patch Details 
diff --git a/packages/fern-docs/bundle/src/app/[host]/[domain]/error.tsx b/packages/fern-docs/bundle/src/app/[host]/[domain]/error.tsx
index 996a4b0f3..707d9a88a 100644
--- a/packages/fern-docs/bundle/src/app/[host]/[domain]/error.tsx
+++ b/packages/fern-docs/bundle/src/app/[host]/[domain]/error.tsx
@@ -5,7 +5,7 @@ import GradientExclamation from "@fern-docs/components/GradientExclamation";
 import { HiddenSidebar } from "@fern-docs/components/theming/HiddenSidebar";
 import { useEffect } from "react";
 
-import { NotFound404Tracker } from "@/components/analytics/NotFound404Tracker";
+
 import ReturnHomeButton from "@/components/ReturnHomeButton";
 
 export default function ErrorBoundary({ error, reset }: { error: Error & { digest?: string }; reset: () => void }) {
@@ -15,7 +15,6 @@ export default function ErrorBoundary({ error, reset }: { error: Error & { diges
 
     return (
         <>
-            <NotFound404Tracker />
             <HiddenSidebar />
             <div className="flex h-[calc(100svh-var(--header-height)-6rem)] w-screen flex-col items-center justify-center gap-6">
                 <GradientExclamation />

Analysis

Error boundary incorrectly tracks rendering errors as 404 events in analytics

What fails: ErrorBoundary in packages/fern-docs/bundle/src/app/[host]/[domain]/error.tsx uses NotFound404Tracker component, which sends "not_found" events to PostHog for all rendering errors instead of actual 404 scenarios

How to reproduce:

  1. Trigger any rendering error in a [host]/[domain] route (e.g., component crash, JavaScript error)
  2. Check PostHog analytics - error will be logged as "not_found" event instead of error event

Result: All rendering errors tracked as 404 events, polluting 404 analytics and making it impossible to distinguish actual missing pages from component failures

Expected: Error boundaries should not track analytics events, consistent with other error boundaries in the codebase (see packages/fern-docs/bundle/src/app/error.tsx which has no analytics tracking). NotFound404Tracker should only be used in actual not-found.tsx files per its JSDoc documentation: "Should be added to not-found pages to capture analytics when users hit a 404"

<HiddenSidebar />
<div className="flex h-[calc(100svh-var(--header-height)-6rem)] w-screen flex-col items-center justify-center gap-6">
<GradientExclamation />
<div className="flex flex-col text-center">
<h1>We&apos;ve encountered an error!</h1>
<p className="text-(color:--grayscale-a9)">Please try again. If the problem persists, contact support.</p>
</div>
<div className="flex flex-col gap-3 sm:flex-row">
<FernButton intent="primary" onClick={reset}>
Try again
</FernButton>
<ReturnHomeButton />
</div>
</div>
</>
);
}
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